@article {MR2608124,
AUTHOR = {Beauchard, Karine and Coron, Jean-Michel and Rouchon, Pierre},
TITLE = {Controllability issues for continuous-spectrum systems and ensemble controllability of {B}loch equations},
JOURNAL = {Comm. Math. Phys.},
FJOURNAL = {Communications in Mathematical Physics},
VOLUME = {296},
YEAR = {2010},
NUMBER = {2},
PAGES = {525--557},
ISSN = {0010-3616},
CODEN = {CMPHAY},
MRCLASS = {93B05 (35Q40 81Q93)},
MRNUMBER = {2608124},
DOI = {10.1007/s00220-010-1008-9},
URL = {http://dx.doi.org/10.1007/s00220-010-1008-9}, }